Pro-Gaddafi guards have raped child detainees, and Libyan rebels are abusing children and holding migrant workers as prisoners, Amnesty International charged, calling on both sides to respect prisoners.

The London-based rights group said it gathered testimony from prisoners and survivors of the conflict in the capital Tripoli, where rebel forces have been clashing with remnants of Muammar Gaddafi's regime in a battle for control of the city.

Amnesty said its delegation uncovered evidence of rape being committed against inmates of Tripoli's Abu Salim Prison while it was under the control of Gaddafi forces.

Two boys told cellmates that they had been raped numerous times by a guard, the Amnesty statement said.

An unnamed detainee said one of the boys returned to his cell almost naked with his clothes torn one night. He told the detainee he had been raped.

Other detainees said they were beaten in pro-Gaddafi prisons with metal wires, sticks and batons were given electric shocks.

One boy, whose name was not released, told Amnesty that he responded to calls by Gaddafi's regime for volunteer fighters. He said he was handed a Kalashnikov rifle that he did not know how to use and was driven to the western city of Zawiya.

He said he fled the fighting after Nato began bombing a camp that soldiers were using. He said rebels found him unarmed but shot him in the knee at close range.

"I fell on the ground, and they continued beating me with the back of their rifles all over my body and face," he said.

Amnesty said that despite repeated promises by the opposition's National Transitional Council that its forces would not repeat the same human rights violations of the former regime, its observers found some 125 people held in an overcrowded cell with barely enough room for detainees to move.

Also, several detainees held in detention centres by the opposition said they were migrant workers, not fighters.

Gaddafi's regime recruited foreign mercenaries from Chad and other neighbouring African countries to try to put down the uprising.

The African nationals said that they remain in custody only because of their skin colour.

No comment on the Amnesty report was immediately available from either side.